1. Technical Field
This invention relates to heating systems for injection molds and more particularly to the system and methods of forming the heating assemblies that supply heat to the plastic materials used to mold components which are fed through complex manifold delivery paths to the nozzles disposed in the mold.
2. Discussion
The condition of the molding material that is delivered to a mold cavity is critical to the quality of the component that comes out of the mold. The reference to the condition of a fluid means at least the desired temperature of the fluid to obtain optimum molding quality for the components. Injection molds typically mold large numbers of components with each injected feed cycle to provide high capacity production of the molded parts. The molding material typically is a molten plastic material which is fed from a primary supply to a series of distributor manifolds which in turn feed an array of injection nozzles that inject the plastic into the mold cavity.
It is essential that the molding material injected into the molds be at the proper temperature notwithstanding the fact that it travels over a serpentine path from the primary supply to the feed manifolds and into the mold cavity. Temperature differences within the molten plastic delivered to different cavities can result in different fill rates and hence different weights for the components or it may cause the molten plastic to overheat and degrade. Another problem is that it may be at too low a temperature causing similar problems or result in the use of excessive pressures.
The use of a series of manifolds to supply large number of mold cavities simultaneously is a standard production requirement. It therefore becomes necessary for the injection mold heat assembly to be designed to avoid the aforementioned failure conditions that could result when the fluid is not properly heated. The design of such heating systems desirably should be more than just meet heating requirements. The building of the system should also desirably be low in cost which translates into simple construction techniques that can be accomplished in very short periods of time and are not overly complicated. Another requirement for these heating systems is that replacement of burned out heaters be easily maintained and quickly reassembled without requiring inordinate down time of the injection molding machines.
Previously known systems, while effective in terms of the temperature control, were unduly expensive, and due to the complexity required long periods of time to assemble the systems as well as replacement and to reassemble. The conventional approach in these prior heating systems is to enclose or contain a heating element in a heat conductive conduit that is then secured in the heating block of the distribution manifold. The heating block is adapted to provide the essential thermal control for the multiple fluid delivery stations embodied in the manifold but simultaneously feed multiple cavity molds.
It has been known to enclose the heating element in a pair of separable abutting members that form a hole when the upper and lower portions of the abutting members are combined to carry the heating element. Referring to FIG. 1 there is shown a heat conductive conduit that has been formed from separable abutting members described in U.S. Pat. No. 5,539,857 assigned to the same assignee as the instant invention. Prior art FIG. 1 illustrates the serpentine heat conductive conduits that are constructed in the heating block in order that it trace the fluid delivery path from the molten plastic supply to the injection molding stations. Assembly of the abutting parts X and Y and then enclosing the heater units which can then be fixed into a serpentine heating channel required that they be assembled in multiple sections. A continuous length of abutting members X and Y could not easily be bent once assembled with the heating element or properly shaped to fit into the serpentine heating paths in the heating block without first forming individual sections A through J as identified in FIG. 1 which are then pieced together. The largest conductive conduit section was generally a "U" shaped or loop configuration. This separable abutting type construction was costly, time consuming but at the time it was an improvement to the then existing techniques.
What is required is a low cost, simple to assemble and replace heating assembly, that can be assembled in a very short period of time and is effective in providing the needed thermal control for the flowable molten plastic that forms the molded components.